Federal prosecutors in New Jersey are investigating Port Authority Chairman David Samson’s overlapping public and private interests, a source said Tuesday, on the eve of a commissioners’ meeting at which protesters are expected to repeat calls for Samson’s resignation.

The U.S. attorney for New Jersey issued a subpoena requesting documents related to Samson's involvement in agency votes that benefited clients of his powerful law firm, Wolff & Samson, a source familiar with the matter who would only speak on condition of anonymity said.

The subpoena, which was issued early last week, appears to expand U.S. Attorney Paul Fishman’s investigation beyond the September lane closures at the George Washington Bridge and into the chairman’s business dealings.

“We don’t comment on any investigations,” Samson’s attorney, Michael Chertoff, said in a statement.

A similar subpoena was issued by federal prosecutors in Manhattan earlier this month but was quickly withdrawn, as authorities in New York agreed to cede the investigation to their counterparts across the Hudson River. Fishman had already begun a review of the lane closures that were ordered by David Wildstein, another Christie ally at the Port Authority.

Samson has come under fire for his vote on a $256 million reconstruction of the rundown PATH station in Harrison three months after a builder represented by Wolff & Samson proposed converting a nearby warehouse into hundreds of luxury apartments.

Records show Samson also voted to reduce a yearly lease payment from more than $900,000 to $1 for a park-and-ride lot in a deal with NJ Transit. At the time, NJ Transit was paying his firm up to $1.5 million for work related to maximizing profits on park-and-ride lots. After The Record reported on that issue, Samson said he had meant to recuse himself from the vote.

A subcommittee of the Port Authority’s Board of Commissioners is scheduled to reconsider the lease deal this morning, before the board meets later Wednesday.

Samson also voted on two bridge contracts worth $2.8 billion that went to construction companies represented by his firm. A person briefed on the subpoena said it requested documents related to those decisions, and possibly others.

About 30 protesters will be posted outside that meeting to call for Samson’s resignation, according to the New Jersey Working Families Alliance, which is organizing the protest. The group describes itself as an association of union organizers and environmentalists and is affiliated with nearly a dozen public and private sector unions.

“You really see this groundswell of opposition to him remaining as chairman of the Port Authority, and I think tomorrow's protest will demonstrate that,” Rob Duffey, communications director of the New Jersey Working Families Alliance, said Tuesday.

The group filed an ethics complaint against Samson earlier this month, arguing he violated the state’s conflict of interest law by getting involved in Port Authority votes that benefited clients of his law firm.

"These ethical lapses, or the allegations that we make in this complaint, demonstrate a clear violation of the public trust,” Duffey said.

Duffey said his group’s position mirrored that of Patrick Foye, the executive director of the Port Authority. Foye, who was appointed by New York’s Democratic governor, said last month that he did not believe Samson had the “moral authority” to lead the agency.

Samson’s actions at the authority have come under scrutiny since the George Washington Bridge lane closure scandal became national news. Local access lanes in Fort Lee were shut down for four days in September, causing huge traffic jams in the borough, apparently in retribution for the Democratic mayor’s failure to endorse Christie’s reelection campaign.

Meanwhile, Christie’s former campaign manager Bill Stepien, who is also the subject of a federal investigation into the lane closures, according to his attorney, found a new job at a top political consulting firm despite the controversy.

Stepien now works for FLS Connect, a Minnesota-based vendor for the Republican Party, the company confirmed on Tuesday. The Republican National Committee paid the firm more than $67 million between 2008 and this year, according to data compiled by The Center for Responsive Politics. It made more than $20 million from Mitt Romney’s presidential campaign in 2012. The firm specializes in telephone calls for fundraising, advertising, voter identification or tele-town hall meetings.

“FLS Connect is excited to have Bill Stepien join our team,” the firm’s president, Sheila Berkley, said in a statement. “His extensive national experience and knowledge will be an asset to our clients and our company.”

The job signals a possible return to high-profile Republican politics for Stepien, although back in New Jersey, his attorney was still fighting a court battle to keep Stepien from having to turn over documents to a panel of state lawmakers investigating the lane closures. A Superior Court judge in Mercer County is expected to rule by the end of the month at the earliest on whether Stepien and former Christie deputy chief of staff Bridget Anne Kelly must comply with a subpoena for documents.

Stepien ran Christie’s successful campaigns for governor in 2009 and last year, and he was seen as a rising star in the national Republican Party. After Christie won by a 42-point margin in November, he signed on as a consultant with the Republican Governors Association, which Christie chairs.

But Stepien broke his ties with the association after documents became public earlier this year showing Christie’s top Port Authority appointees kept Stepien updated on the fallout from their closure of the bridge access lanes.

Stepien could not be reached for comment on Tuesday, and FLS Connect did not comment beyond its statement. Stepien’s job with the firm was first reported by Politico.